1. Field of the Invention
This invention relates to an alignment apparatus of a noncontact type tonometer including a target projecting system for projecting light emitted from a light emitting source to an eye to be tested along the axial line of a fluid discharging nozzle adapted to discharge fluid and forming a target image on the eye, and an alignment light receiving optical system for receiving the target image along the axial line of the nozzle and forming the target image on a light receiving sensor.
2. Prior Art of the Invention
Heretofore, an alignment apparatus of a noncontact type tonometer includes a target projecting system for projecting a target image toward the center of curvature of the cornea of an eye to be tested along the axial line of a nozzle for discharging fluid such as air, etc., and a light receiving optical system for receiving a reflecting light reflected by the target image on the cornea along the axial line of the nozzle with a light receiving sensor thereof. And, the light receiving sensor is located in position where a light receiving quantity of more than a predetermined value of a reflecting light reflected by the target image when the alignment axial line of the eye and the axial line of an air pulse discharging nozzle are in alignment with each other and the distance between the eye and the nozzle is a predetermined distance. And, the alignment apparatus outputs an alignment completion signal when the light receiving quantity of the light receiving sensor reaches a predetermined value or more.
However, the conventional alignment apparatus of a non-contact type tonometer had such a problem as that since the alignment is determined by the received light quantity, the light receiving quantity of the light receiving sensor becomes a predetermined value or more and an alignment completion signal is issued when the alignment has not been completed, particularly in such events as that the cornea is suffered from a disturbance light or the eye to be tested is high in reflectance. Also, in the event that the cornea is low in reflectance, since the received light quantity does not become a predetermined value or more when the alignment has been completed, an alignment completion signal is not issued and it does not go to the eye pressure measuring step.